It's as if someone has freed me from invisible chains. My home circuit, a narrow technical singletrail, suddenly feels completely different: much smoother and faster. My key fear section flies past me. Not long ago, I hit the root with my pedals so hard that I went over the handlebars in a high arc. Almost four centimetres more between the crank and the ground now give me the freedom to keep the chain under constant tension. At first I hesitated to simply pedal through and over everything. Now I feel more confident with every metre. Even on bends or steps, I don't need to stop pedalling. The motor constantly transmits its power to the rear wheel, which provides continuous traction. Short e-bike cranks are worth their weight in gold - why didn't I think of this much earlier?
Very simple: tuning with a short e-bike crank
The heyday of tuning is long gone for classic mountain bikes. Back then, when German backyard tinkerers showed the big Japanese how to build brakes and tune forks with self-wound steel springs, there was still a lot to be gained. Today, the devices are largely mature, tuning is mostly reduced to visual measures and customisation, without any relevant gain in performance. E-MTBs are a different story. Some of the technology is still in its infancy. This is because e-bikes are developed several years in advance. While conventional mountain bikes are based on decades of experience, some areas of e-mountain bikes still lack extensive practical experience. Only now have the necessary kilometres been accumulated and some correlations are becoming clearer. One of these kilometre eaters is bike developer Lutz Scheffer. This year alone, the Garmisch resident by choice covered almost 300,000 metres in altitude on his e-mountainbike. Scheffer was also the first to scour the market for shorter e-bike cranks. He found what he was looking for in the unicycle scene. The Spirit Signature crank from unicycle guru Chris Holm with an Isis mount was the only available short crank that fitted Scheffer's Bosch motor.
Back to my test ride: fitting the tuning crank is done in ten minutes with the right tools (see workshop). The familiarisation phase from 175 millimetres to the short version (137 mm) is surprisingly short. The feeling of sitting on a children's bike disappears with every turn of the pedals, after which the significantly faster pedalling feels completely normal. Switching back from short to long is much more difficult: you suddenly feel completely unergonomic - as if you have to set a huge wheel in motion.
How to ride short e-bike cranks on an e-mountainbike
The aha moment comes on the singletrail. My e-MTB, which is often in contact with the ground due to the low bottom bracket, suddenly feels completely different. The dangerous touching down on roots or boulders is as good as a thing of the past. Steps that used to require timing and a sophisticated trial technique can now be mastered with ease because you can keep the chain under constant tension.
However, the maximum power - and you only notice this when you are pedalling up very steep climbs in the lowest gear - drops noticeably. On ramps that I can easily master with the long cranks in turbo mode, I quickly run out of steam with the short cranks. The logical consequence: fit a smaller sprocket at the front. With 14 teeth on the cranks and 42 teeth at the rear, I can climb my home ramps again as usual. If the step to a 137 mm crank is too radical for you, the component manufacturers also offer intermediate sizes.
Test conclusion on short cranks on an e-mountainbike
The steepest climbs are theoretically possible with an e-mountainbike. Thanks to the motor assistance, power is rarely the limiting factor. But as soon as you hit the trails, steps, rocks and roots become stumbling blocks due to the lack of ground clearance. Shorter cranks on the e-bike bring a significant improvement compared to the conventional 175 or 170 millimetre models - and they enable a completely new riding style: constant pressure on the pedals, even corners can be negotiated at an angle. However, if you are often travelling on steep terrain, you should also upgrade to a higher gear ratio. With Bosch drives, sprocket sizes of up to 13 teeth are possible at the front.
Interview with Lutz Scheffer, bike designer and E-MTB tinkerer
EMTB: Lutz, how did you come up with the idea of short e-bike cranks?
Lutz Scheffer: The unique thing about E-MTBs is that you can ride steep and difficult trails. However, you have to pedal constantly. The trails where I live in Garmisch are really tough, and a fall on the downhill side can be really dangerous. These uphill crashes are almost always caused by pedal contact. After a few serious crashes, it was clear to me: I need short cranks. After many attempts with different lengths, I ended up with the 137s from Chris Holm.
Why can't you just set the bottom bracket higher?
Most E-MTBs already have very high bottom brackets anyway. A sensible dimension for me seems to be around 350 mm so that the overall centre of gravity doesn't get too high. If you subtract the crank length and the SAG from this height, my bike with the short cranks gives me a ground clearance of 150 mm instead of the previous 115 mm. With every millimetre more, the pedal clipping rate increases dramatically.
Do the short cranks on the e-bike have any disadvantages?
Yes, with the same cadence the performance drops. If you are travelling in the high Alps and often ride very steep climbs, you need a really low gear ratio. In normal terrain, you can compensate for the lack of power with higher revs: Power is torque times speed. The shorter crank is fully compensated for by a 20 per cent increase in speed. So you just have to pedal faster on the e-bike, which takes some getting used to.
Effects on the height of the empire?
I didn't want to believe it myself. On my reference route to the Reintalangerhütte, I needed exactly 58 minutes. At the end of the tour, I always measured exactly the same battery consumption for all crank lengths.
>> If you and your e-MTB are more at home on steep sections, then it is also worth changing the gear ratio. With a smaller chainring, such routes can be mastered in a much more battery-saving way: Changing the gear ratio on an E-MTB: how to convert quickly and easily.
>> If you've been annoyed by your hands falling asleep on the e-MTB handlebars for a while or your bum hurts even on the third saddle, then our tips for e-bike fitting may be just the solution: Set up your E-MTB correctly: Cockpit, saddle and suspension.
>> After the fitting is before the first tuning. Because there is always something to optimise on an e-mountainbike. Be inspired by our 10 suggestions for a lighter bike: Legal e-bike tuning: How to make your e-MTB lighter.
